This book constitutes the refereed proceedings of the 23rd International Conference on Principles and Practice of Multi-Agent Systems, PRIMA 2020, held in Nagoya, Japan, in November 2020. The 19 full papers presented and 13 short papers were carefully reviewed and selected from 50 submissions.Due to COVID-19, the conference was held online.The conference covers a wide range of ranging from foundations of agent theory and engineering aspects of agent systems, to emerging interdisciplinary areas of agent-based research.

Policy Advisory Module for Exploration Hindrance Problem in Multi-agent Deep Reinforcement Learning.- Analysis of Coordination Structures of Partially Observing Cooperative Agents by Multi-Agent Deep Q-Learning.- Policy Adaptive Multi-Agent Deep Deterministic Policy Gradient.- Multi-Agent Planning with High-Level Human Guidance.- Preference Elicitation in Assumption-Based Argumentation.- Declarative Preferences in Reactive BDI Agents.- Predicting the Priority of Social Situations for Personal Assistant Agents.- Mutex Propagation for SAT-based Multi-Agent Path Finding.- A SMT-based Implementation for Safety Checking of Parameterized Multi-Agent Systems.- A Goal-Based Framework For Supporting Medical Assistance: The Case of Chronic Diseases.- Optimal Control of Pedestrian Flows by Congestion Forecasts Satisfying User Equilibrium Conditions.- Automated Negotiation Mechanism and Strategy for Compensational Vehicular Platooning.- A Cognitive Agent Framework in Information Retrieval: Using User Beliefs to Customize Results.- Deep Reinforcement Learning for Pedestrian Guidance.- NegMAS: A platform for automated negotiations.- Simulation of Unintentional Collusion Caused by Auto Pricing in Supply Chain Markets.- Construct an Artificial Population with Urban and Rural Population Differences Considered: to support long-term care system evaluation by agent-based simulation.- Multi-Agent Path Finding with Destination Choice.